A novel ribbon drive and tensioning system is provided for a print and apply engine, a thermal printer or any other printer which utilizes a ribbon having a medium thereon which can be transferred, such as ink, wax, a polymer material, dye, etc., onto a label. The present system significantly increases label throughput without sacrificing registration of the printed image on the label. To accomplish this, faster acceleration and deceleration ramps, a ramp being defined as a graph of velocity versus time, are provided. To enable faster ramps, while not affecting image registration on the label, the inertial ribbon tension variances associated with starting and stopping the rotation of the supply and take-up ribbon rolls in the ribbon system were decreased and the ribbon tension changes that occur as the ribbon roll diameter changes were minimized. This improves image registration and controls “smudging: or “scuffing” of the printed image on the label.
The present ribbon drive and tensioning system maintains uniform ribbon tension as the ribbon roll diameter varies as ribbon unwinds from the ribbon supply spindle and rewinds on the ribbon take-up spindle and enables faster acceleration/deceleration ramps by minimizing the inertial effects of the ribbon rolls and their spindles through the use of positional servo-controlled dancing arms. The present system also enables operation with longer length/larger diameter (higher inertia) ribbon rolls, thereby requiring fewer ribbon changeovers.
In prior art systems, the platen roller drives the media which, in turn, drives the ribbon through friction. Differential ribbon tension across the platen roller causes micro-slippage that adversely affects image registration on the label. Large instantaneous ribbon tension changes, like those associated with acceleration and deceleration ramps and the high inertia of the ribbon spindles, can cause image registration errors. In some situations, slack ribbon loops can occur which create ribbon tension spikes that can cause smudge or scuff marks on the label due to high ribbon slip rates if the slack is rapidly taken up. Prior art thermal printers and print and apply printers typically use slip clutches or torque motors to maintain ribbon tension. In these systems, the input/output ribbon tension varies with the changing diameters of the supply and take-up ribbon rolls. In some prior art printers, DC torque motors vary torque proportional to the ribbon roll diameter to maintain more uniform ribbon tension, however, the corrections are not ideal. Tension changes with different diameters still exist. In addition, the DC torque motors add inertia which increases inertial tension variance.
The present system uses positional (tension) servo-controlled dancing arms at both the ribbon supply and the ribbon take-up spindles to control the ribbon tension, thereby isolating the causes for tension errors present in prior art thermal printers. The low inertia dancing arms of the present invention absorb ribbon impulses during acceleration/deceleration ramps. There are no tension changes caused by the high inertia ribbon spindles and their DC drive motors because of the isolation provided by the dancing arms. Because the dancing arms create the ribbon tension, there is no tension change as the ribbon roll size changes.